1. Field of the Invention
The present invention relates to a method of grinding a half toroidal CVT disk used as a continuously variable transmission in an automobile.
2. Description of the Related Art
A half toroidal CVT disk includes a disk-shaped disk main body 1; and, as shown in FIG. 5, the disk main body 1 has an inner surface portion 2 consisting of a through hole formed in the central portion thereof, an outer surface portion 3, and a toroidal surface 4 formed on one surface of the disk main body 1. On one end side of the inner surface portion 2, there is formed an inner surface involute spline portion 5; and, on the other end side thereof, there is formed an inside diameter surface 6. And, the toroidal surface 4, inner surface involute spline portion 5 and inside diameter surface 6, except for the outer surface portion 3, must be respectively ground so as to have concentricity accuracy of a given value or higher.
For this reason, conventionally, for example, as disclosed in JP-A-2000-271844, in a state where the outer surface portion 3 is centered with the inner surface involute spline portion 5 as the standard thereof and is chucked in the thus centered state, the outer surface portion 3 is ground; and, with the thus ground outer surface portion 3 as the standard thereof, the toroidal surface 4 and inner surface portion 2 are respectively ground in separate steps.
Also, as a compound grinding machine, conventionally, there is known a compound grinding machine which, as disclosed in JP-A-10-235545, comprises a plurality of spindle devices each including a work chuck for chucking a work, while these spindle devices are carried on a swing table which is capable of indexingly swinging in such a manner to be able to correspond to a plurality of operation positions. At these operation positions, there are disposed two or more kinds of grinding devices and, using the grinding devices, the works chucked by the work chucks are respectively ground to thereby shorten the grinding time.
In case where the toroidal surface and inner surface portion of the half toroidal CVT disk are ground in separate steps, it is necessary to grind the outer surface portion as the common standard surface for securing the concentricity of these grinding surfaces. However, to grind the outer surface portion is not necessary for the function of the half toroidal CVT disk and thus the step of grinding the outer surface portion provides a great factor in the increased cost of the half toroidal CVT disk.
Also, there must be secured concentricity between the inner surface involute spline portion to be worked prior to the heat treatment of the half toroidal CVT disk and the toroidal surface and inner surface portion to be ground.
Further, in case where the outer surface, inner surface portion and toroidal surface are ground sequentially in separate steps, the half toroidal CVT disk not only must be mounted onto and removed from the grinding machines but also must be delivered between the grinding machines in these respective grinding steps, which makes it troublesome to grind the half toroidal CVT disk and thus provides an important factor in the increased cost thereof.
Still further, in the case of the toroidal surface grinding operation, there is a limit on the diameter of a grinding wheel and the direction of the rotary shaft of the grinding wheel must be set at an angle of 58xc2x0-65xc2x0 (xc2x115xc2x0) with respect to the direction of the rotary shaft of the work.
The present invention aims at eliminating the drawbacks found in the above-mentioned conventional half toroidal CVT disk grinding methods. Accordingly, it is a main object of the invention to provide a half toroidal CVT disk grinding method which can secure concentricity between the inner surface portion and toroidal surface of the half toroidal CVT disk while omitting the step of grinding the outer surface portion thereof, thereby being able to reduce the number of manufacturing steps of the half toroidal CVT disk and thus the manufacturing cost thereof.
Also, it is a second object of the invention to provide a half toroidal CVT disk grinding method which is capable of not only grinding the inner surface portion and toroidal surface of the half toroidal CVT disk simultaneously using a compound grinding machine while they remain chucked by the same chuck mechanism but also securing concentricity between the inner surface portion and toroidal surface.
Further, it is a third object of the invention to provide a half toroidal CVT disk grinding method which, in case where the inner surface portion of the half toroidal CVT disk is hard broached after the half toroidal CVT disk is thermally treated, can grind the toroidal surface of the half toroidal CVT disk with the thus hard broached inner surface portion as the standard thereof to omit the step of grinding the outer surface portion the half toroidal CVT disk, thereby being able to reduce the number of manufacturing steps of the half toroidal CVT disk and thus the manufacturing cost thereof.
In attaining the above objects, according to a first aspect of the invention, there is provided a method of grinding a half toroidal CVT disk by a grinding mechanism with a tool for grinding the half toroidal CVT disk, the half toroidal CVT disk having an inner surface portion, an outer surface portion and a toroidal surface having a given machining allowance, the method including the steps of: centering the half toroidal CVT disk with a first part of the inner surface portion worked prior to the heat treatment of the half toroidal CVT disk as the standard thereof; chucking the centered half toroidal CVT disk by a chuck mechanism; grinding the toroidal surface of the chucked half toroidal CVT disk in a state that one of the half toroidal CVT disk and the tool is inclined at a given angle with respect to the other; and grinding a second part of the inner surface portion simultaneously with the toroidal surface in a compound manner.
Further, according to a second aspect of the invention, there is provided a method of grinding a half toroidal CVT disk by a grinding mechanism with a tool for grinding the half toroidal CVT disk, the half toroidal CVT disk having an inner surface portion, an outer surface portion and a toroidal surface having a given machining allowance, the method comprising the steps of: hard-broaching the inner surface portion after the heat treatment of the half toroidal CVT disk; centering the half toroidal CVT disk with the hard broached inner surface portion as the standard thereof; chucking the centered half toroidal CVT disk by a chucking mechanism; and grinding the toroidal surface of the chucked half toroidal CVT disk in a state that one of the half toroidal CVT disk and the tool is inclined at a given angle with respect to the other.
Now, according to the first aspect of the invention, the half toroidal CVT disk is centered with the inner surface portion worked prior to the heat treatment of the half toroidal CVT disk as the standard thereof and is chucked in the thus centered state by the chuck mechanism and, in the centered state, the toroidal surface is ground. Thanks to this, even in case where the step of grinding the outer surface portion of the half toroidal CVT disk is omitted, there can be secured concentricity between the inner surface portion and toroidal surface of the half toroidal CVT disk. This can decrease the number of manufacturing steps of the half toroidal CVT disk, so that the manufacturing cost of the half toroidal CVT disk can be reduced. Further, when the toroidal surface is ground, the inner surface portion is ground simultaneously in a compound manner. This makes it possible not only to secure concentricity between the inner surface portion and toroidal surface of the half toroidal CVT disk but also to shorten the grinding operation time, thereby being able to reduce the manufacturing cost of the half toroidal CVT disk.
Further, according to the second aspect of the invention, in case where the inner surface portion is hard broached after the heat treatment of the half toroidal CVT disk, in a state where the half toroidal CVT disk is centered with the thus hard broached inner surface portion and is chucked in the thus centered state by the chuck mechanism, the toroidal surface is ground. Due to this, there is eliminated the step of grinding the outer surface portion of the half toroidal CVT disk to thereby decrease the number of manufacturing steps of the half toroidal CVT disk, so that the manufacturing cost of the half toroidal CVT disk can be reduced.